Lung cancer is the leading cause of death from cancer in North America, and it has the second most common cancer incidence among both men and women. One in 11 Canadian men will develop lung cancer, and 1 in 12 will die from this condition, while one in 19 Canadian women will develop lung cancer, and 1 in 22 will die from this disease. Lung cancer also results in the most lost years of life due to cancer death in both men and women. The best outcome of lung cancer treatment is achieved when the lesion is discovered in the pre-invasive stage, which is also commonly referred as carcinoma in situ (CIS).
Early and accurate diagnosis of lung cancer offers a better chance of cure, results in the use of less radical treatment methods, and reduces the cost of treatment. The five-year survival for all stages of lung cancer is only 11-14 percent, while for Stage I it is 42 to 47 percent. Under optimal conditions, survival can be even higher. However, with respect to currently available lung imaging techniques, lung cancer is generally asymptomatic until it has reached an advanced stage, when the treatment outcome is poor. In particular, very early lung cancers are difficult to detect and localize by conventional white-light endoscopy since these cancers are only a few cell layers thick and LIP to a few millimeters in surface diameter, producing insufficient changes to make them visible under white light illumination. In the lung, only about 30 percent of CIS lesions are visible by conventional white-light bronchoscopy.
In the past decade, tissue autofluorescence imaging has been successfully used to improve the early detection of lung cancers. However, fluorescence endoscopy technology (developed at B.C. Cancer Agency and also referred as “LIFE” technology) has less optimal specificity for lung cancer detection (66 percent for LIFE compared to 90 percent for conventional white light bronchoscopy) although it improved the sensitivity from 25 percent for white light bronchoscope to 67 percent for LIFE. There is still much room for improvement in the diagnostic accuracy.
Recently, we have performed Raman spectroscopy measurements on fresh biopsy bronchial tissue samples and found significant spectral differences between normal and malignant lung tissues, demonstrating the potential of Raman spectroscopy for in vivo lung cancer detection.
In contrast to fluorescence technology, Laser-Raman spectroscopy probes molecular vibrations and gives very specific, fingerprint-like spectral features and has high accuracy for differentiation of malignant tissues from benign tissues. Raman spectroscopy can also be used to identify the structural and compositional differences on proteins and genetic materials between malignant lung cancers, their pre-cursers, and normal lung tissues. This knowledge will lead to better understanding, on the biochemical bases, of the evolution process of lung cancers from benign to malignancy. The biochemical information obtained from in vivo Raman measurements may also be helpful for predicting the malignancy potential of pre-invasive and invasive lung cancers. The objective of this invention is to develop a miniaturized laser-Raman probe, which can go through the instrument channel of a bronchoscope to perform Raman spectroscopy measurements of the bronchial tree in vivo. A further objective is to enable the application of Raman spectroscopy for in vivo lung cancer detection and evaluation, therefore, improve the specificity of lung cancer detection and the overall detection accuracy when combined with fluorescence endoscopy technology.
When monochromatic light strikes a sample, almost all the observed light is scattered elastically (Rayleigh scattering) with no change in energy (or frequency). A very small portion of the scattered light, about 1 in 108, is inelastically scattered (Raman scattering) with a corresponding change in frequency. The difference between the incident and scattered frequencies corresponds to an excitation of the molecular system, most often excitation of vibrational modes. By measuring the intensity of the scattered photons as a function of the frequency difference, a Raman spectrum is obtained. Raman peaks are typically narrow (a few wavenumbers) and in many cases can be attributed to the vibration of specific chemical bonds (or normal mode dominated by the vibration of a single functional group) in a molecule. As such, it is a “fingerprint” for the presence of various molecular species and can be used for both qualitative identification and quantitative determination.
In recent years, Raman spectroscopy has been investigated for in vitro diagnosis of malignancies in various organs (e.g., brain, breast, bladder, colon, larynx, cervix, and skin). These studies show that features of tissue Raman spectra can be related to the molecular and structural changes associated with neoplastic transformations. A sensitivity and specificity of 82 percent and 92 percent respectively for differentiating between cervical precancerous and other tissues in vitro have been reported. Mahadevan-Jansen, Raman spectroscopy for the detection of cancers and precancers, J BIOMED. OPT. 1, 31-70, 1996.
In vivo NIR Raman measurements have also been reported in the cervix, colon, esophagus, and the skin. Mahadevan-Jansen, Development of a fiber optic probe to measure NIR Raman spectra of cervical tissue in vivo, PHOTOCHEM. PHOTOBIOL. 68: 427-431, 1998; Shim, In vivo near-infrared Raman spectroscopy: demonstration of feasibility during clinical gastrointestinal endoscopy, PHOTOCHEM. PHOTOBIOL. 72: 146-150, 2000; Huang, Rapid near-infrared Raman spectroscopy system for real-time in vivo skin measurements, OPT. LETT. 26: 1782-1784, 2001; Utzinger, Near-infrared Raman spectroscopy for in vivo detection of cervical precancers, APPL. SPECTROSC. 55:955-959, 2001.
Shim et al. have shown differences for in vivo Raman spectra among normal, precancerous, and cancerous esophageal and gastric tissues. Raman spectroscopy of lung tissues, however, has only been reported on formalin-fixed parenchyma lung diseases, which provide very limited guidance to in vivo applications due to the adverse effect of formalin fixation on tissue Raman spectra. Kaminaka, Near-infrared Raman spectroscopy of human lung tissues: possibility of molecular-level cancer diagnosis, J. RAMAN SPECTROSC. 32:139-141, 2001; Kaminaka, Near-infrared multichannel Raman spectroscopy toward real-time in vivo cancer diagnosis, J. RAMAN SPECTROSC. 33:498-502, 2002; Shim, The effects of ex vivo handling procedures on the near-infrared Raman spectra of normal mammalian tissues, PHOTOCHEM. PHOTOBIOL. 63: 662-671, 1996.
The development of an in vivo tissue Raman probe is technically challenging due to the weak Raman signal of tissue, interference from tissue fluorescence and spectral contamination caused by the background Raman and fluorescence signals generated in the fiber itself. Most probes published in literature and commercial products are larger than 10 mm in diameter, and therefore are not suitable for endoscopy applications. The instrument channel of commonly-used bronchoscopes are 2.2 mm (for example, Olympus BF-20, BF-40).
To date, the only endoscopic probe utilized for in vivo measurements is the Enviva Raman probe manufactured by Visionex, Inc., Atlanta, Ga. However, the company was dissolved two years ago; therefore, the probe is no longer commercially available. That probe consisted of a central delivery fiber (400 μm core diameter) surrounded by seven collection fibers (300 μm core diameter). It incorporated LP filters in the collection fibers and a BP filter in the delivery fiber. The main disadvantages of that probe are that (1) only seven collection fibers were used, which cannot fill the full vertical height of the CCD sensor in the spectrometer; therefore, it was unable to gain the maximum sensitivity; and (2) the size of the collection fibers was big (300 μm), leading to poor spectral resolution (>20 cm−1).